• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.179-200
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• 1996

The intrinsic instabilities of fluid flow occurred in the melt of the Czochralski crystal growth system Czochralski method, asymmetric flow patterns and temperature profiles in the melt have been studied by many researchers. The idea that the non-symmetric structure of the growing equipment is responsible for the asymmetric profiles is usually accepted at the first time. However further researches revealed that some intrinsic instabilities not related to the non-symmetric equipment structure in the melt could also appear. Ristorcelli had pointed out that there are many possible causes of instabilities in the melt. The instabilities appears because of the coupling effects of fluid flow and temperature profiles in the melt. Among the instabilities, the B nard type instabilities with no or low crucible rotation rates are analyzed by the visualizing experiments using X-ray radiography and the 3-D numerical simulation in this study. The velocity profiles in the Silicon melt at different crucible rotation rates were measured using X-ray radiography method using tungsten tracers in the melt. The results showed that there exits two types of fluid flow mode. One is axisymmetric flow, the other is asymmetric flow. In the axisymmetric flow, the trajectory of the tracers show torus pattern. However, more exact measurement of the axisymmetrc case shows that this flow field has small non-axisymmetric components of the velocity. When fluid flow is asymmetric, the tracers show random motion from the fixed view point. On the other hand, when the observer rotates to the same velocity of the crucible, the trajectory of the tracer show a rotating motion, the center of the motion is not same the center of the melt. The temperature of a point in the melt were measured using thermocouples with different rotating rates. Measured temperatures oscillated. Such kind of oscillations are also measured by the other researchers. The behavior of temperature oscillations were quite different between at low rotations and at high rotations. Above experimental results means that the fluid flow and temperature profiles in the melt is not symmetric, and then the mode of the asymmetric is changed when rotation rates are changed. To compare with these experimental results, the fluid flow and temperature profiles at no rotation and 8 rpm of crucible rotation rates on the same size of crucible is calculated using a 3-dimensional numerical simulation. A finite different method is adopted for this simulation. 50×30×30 grids are used. The numerical simulation also showed that the velocity and flow profiles are changed when rotation rates change. Futhermore, the flow patterns and temperature profiles of both cases are not axisymmetric even though axisymmetric boundary conditions are used. Several cells appear at no rotation. The cells are formed by the unstable vertical temperature profiles (upper region is colder than lower part) beneath the free surface of the melt. When the temperature profile is combined with density difference (Rayleigh-B nard instability) or surface tension difference (Marangoni-B nard instability) on temperature, cell structures are naturally formed. Both sources of instabilities are coupled to the cell structures in the melt of the Czochralski process. With high rotation rates, the shape of the fluid field is changed to another type of asymmetric profile. Because of the velocity profile, isothermal lines on the plane vertical to the centerline change to elliptic. When the velocity profiles are plotted at the rotating view point, two vortices appear at the both sides of centerline. These vortices seem to be the main reason of the tracer behavior shown in the asymmetric velocity experiment. This profile is quite similar to the profiles created by the baroclinic instability on the rotating annulus. The temperature profiles obtained from the numerical calculations and Fourier transforms of it are quite similar to the results of the experiment. bove esults intend that at least two types of intrinsic instabilities can occur in the melt of Czochralski growing systems. Because the instabilities cause temperature fluctuations in the melt and near the crystal-melt interface, some defects may be generated by them. When the crucible size becomes large, the intensity of the instabilities should increase. Therefore, to produce large single crystals with good quality, the behavior of the intrinsic instabilities in the melt as well as the effects of the instabilities on the defects in the ingot should be studied. As one of the cause of the defects in the large diameter Silicon single crystal grown by the

• Steel and Composite Structures
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• 제29권5호
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• pp.669-680
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• 2018

The rapidly decreasing natural resources and the global variation of the climate push us to find intelligent and efficient structural systems to provide more people with fewer resources. This paper proposed a kinematic cable-strut system to realize sustainable structures in responding to changing environmental conditions. At first, the concept of the kinematic system based on crystal-cell pyramid (CP) cable-strut unit was given. Then the deployment of the structure was studied experimentally. After that, the static behaviors in the fully deployed state under the symmetric and asymmetric load cases were investigated. Moreover, the effects of thermal loading and the initial prestress distribution were also discussed. Comparative studies between the proposed structure and other deployable cable-strut system under three times of design load cases were carried out. Finally, the robustness of the system was studied by removal of one passive cable at one time.

• 대한임베디드공학회논문지
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• 제14권2호
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• pp.79-86
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• 2019

For decades, in-memory data structures have been designed for DRAM-based main memory that provides symmetric read/write performances and has no limited write endurance. However, such data structures provide sub-optimal performance for NVM as it has different characteristics to DRAM. With this motivation, we rethink a conventional red-black tree in terms of its efficacy under NVM settings. The original red-black tree constantly rebalances sub-trees so as to export fast access time over dataset, but it inevitably increases the write traffic, adversely affecting the performance for NVM with a long write latency and limited endurance. To resolve this problem, we present a variant of the red-black tree called a hierarchical balanced binary search tree. The proposed structure maintains multiple keys in a single node so as to amortize the rebalancing cost. The performance study reveals that the proposed hierarchical binary search tree effectively reduces the write traffic by effectively reaping the high capacity of NVM.

• Steel and Composite Structures
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• 제39권1호
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• pp.1-20
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• 2021

An exact solution based on refined third-order theory (TOT) has been presented for functionally graded porous curved beams having deep curvature. The displacement field of the refined TOT is derived by imposing the shear free conditions at the outer and inner surfaces of curved beams. The properties of the two phase composite are tailored according the power law rule and the effective properties are computed using Mori-Tanaka homogenization scheme. The equations of motion as well as consistent boundary conditions are derived using the Hamilton's principle. The curved beam stiffness coefficients (A, B, D) are obtained numerically using six-point Gauss integration scheme without compromising the accuracy due to deepness (1 + z/R) terms. The porosity has been modeled assuming symmetric (even) as well as asymmetric (uneven) distributions across the cross section of curved beam. The programming has been performed in MATLAB and is validated with the results available in the literature as well as 2D finite element model developed in ABAQUS. The effect of inclusion of 1 + z/R terms is studied for deflection, stresses and natural frequencies for FG curved beams of different radii of curvature. Results presented in this work will be useful for comparison of future studies.

• 대한화학회지
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• 제38권7호
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• pp.485-495
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• 1994

$[M(NO)_2Cl_2]_n(M = Mo, W)$을 출발물질로 사용하여 3단계 합성과정을 거쳐 $[Cl(dppp)(NO)_2M({\mu}-pyz)M'(NO)_2(dppp)Cl][ClO_4]_2$와 $[Cl(phen)(NO)_2M({\mu}-pyz)M'(NO)_2(dppp)Cl][ClO_4]_2$(M,M'= Mo or W; phen = 1,10-phenanthroline; dppp = 1,3-bis(diphenylphosphino)propane; pyz = 1,4-pyrazine) 형의 새로운 대칭 및 비대칭 이핵 착물을 합성하였다. 최종 생성물은 실리카겔 칼럼($2{\times}20$ cm)을 통해 아세톤으로 용리시켜 분리하였다. 합성한 착물은 원소분석과 적외선, 핵사기 공명 및 전자 흡수스펙트럼 등을 이용해서 그 특성을 조사하였다. 적외선 스펙트럼은 모든 착물이 팔면체 구조로서 두 개의 NO기가 cis 위치로 배위되어 있음을 나타냈으며, $^1H$ 및 $^{13}C$ 핵자기 공명 스펙트럼은 이들 착물이 pyz가 다리결합하고 있는 이핵 착물임을 나타내었다.

• Advances in nano research
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• 제16권5호
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• pp.445-458
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• 2024

The objective of this paper is to present free vibration and static stability analyses of rotating composite beams reinforced with carbon nanotubes (CNTs) under uniform thermal loads. Beam structural equations and CNT-reinforced composite (CNTRC) beam formulations are derived based on Timoshenko beam theory (TBT). The temperature-dependent properties of the beam material, such as the elastic modulus, shear modulus, and material density, are assumed to vary over the thickness according to the rule of mixture. The beam material is modeled as a mixture of single-walled carbon nanotubes (SWCNTs) in an isotropic matrix. The SWCNTs are aligned and distributed in the isotropic matrix with different patterns of reinforcement, namely the UD (uniform), FG-O, FG-V, FG- Λ and FG-X distributions, where FG-V and FG- Λ are asymmetric patterns. Numerical examples are presented to illustrate the effects of several essential parameters, including the rotational speed, hub radius, effective material properties, slenderness ratio, boundary conditions, thermal force, and moments due to temperature variation. To the best of the authors' knowledge, this study represents the first attempt at the finite element modeling of rotating CNTRC Timoshenko beams under a thermal environment. The results are presented in tables and figures for both symmetric and asymmetric distribution patterns, and can be used as benchmarks for further validation.

• 전자공학회논문지
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• 제50권3호
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• pp.16-22
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• 2013

n 개의 균일한 결합선로를 해석하기 위하여 2n-port 어드미턴스 매트릭스의 추출에 기초한 일반적인 특성화 절차가 제시된다. 본 논문에서는 비대칭 다중 결합선로를 해석하기 위하여 시간영역의 유한차분법을 사용하여 정규화 모드 파라미터 접근법의 적용을 제안한다. 주파수 의존적인 정규화 모드 파라미터는 2n-port 어드미턴스 매트릭스로부터 얻어지고, 이로부터 주파수 의존적인 전파상수와 유효 유전율 및 결합선로의 특성임피던스를 계산할 수 있다. 이 기법을 설명하기 위해 몇몇의 실질적인 다중 유전체상의 결합선로 구조들이 모의 실험되었으며, 특히 전도체가 유전체 사이에 내재된 형태의 선로가 해석되었다. 시간영역 유한 차분법을 활용한 결과는 Spectral Domain Method의 모의실험 결과와 비교하였고, 잘 일치함을 보였다. 시간영역의 특성화 절차에 기인한 유한차분법은 얇거나 두꺼운 혼성 구조 뿐 아니라 다층 PCB상의 다중의 전도체 결합 선로 설계를 위한 훌륭한 광대역 모의실험 도구가 됨을 볼 수 있다.

• 한국통신학회논문지
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• 제22권9호
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• pp.1968-1974
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• 1997

본 논문에서는 주파수 영역해석법을 사용하여 대칭 및 비대칭 광역 결합 동일평면 도파관 선로의 특성을 연구하였다. 이 구조는 기모드와 우모드 사이의 위상속도비가 크기 때문에 광대역특성과 결합특성을 갖는 마이크로파 회로의 설계에 유용하다. 광역결합 동일평면 도파관 선로내의 스트립의 폭과 슬롯의 폭을 조절하면서 모드 유효유전율과 특성임피던스를 얻었으며 이로부터 효율적인 설계 파라미터를 얻을 수 있다.

• 한국산학기술학회논문지
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• 제11권1호
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• pp.85-91
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• 2010

본 논문에서는 원형편파 변환에 적합한 정사각형 마이크로스트립 안테나를 제안하였다. 제안한 안테나는 접지면의 비대칭 U자형 슬롯의 구조적 특징으로 인하여, 90도의 위상 차이를 갖는 직교전계가 형성되어 원형편파 특성을 형성한다. 또한 비대칭 U자형 슬롯의 대칭축에 따라 원형편파의 방향을 쉽게 조절할 수 있는 장점을 가지고 있다. 비대칭 U자형 슬롯의 대칭축은 두 개의 스위칭 다이오드를 이용하여, 전압조건의 상태에 따라 좌회전편파와 우회전 편파를 각각 실험적으로 구현하였다. 측정된 원형편파의 축비는 2.46 GHz 동작주파수에서 편파방향에 상관없이 약 1.5 dB의 높은 축비특성을 보여주며, 29 MHz (약 1.2 %) 축비 대역폭을 가짐을 실험적으로 확인하였다.

• 대한핵의학회지
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• 제25권2호
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• pp.237-244
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• 1991

$^{99m}Tc-DMSA$ renal scan has been evaluated not only the renal functional cell mass but also some anatomical structures at a loss of the renal parenchymal function. The author classified a renal morphology of the posterior image of $^{99m}Tc-DMSA$ renal scan as the groups of symmetric and asymmetric morphology, the groups of the large, normal and small sized kidneys, the groups of the central photon defects (PD) which could be noted in a dilated pelvocalyceal system due to obstructive uropathy and the cortical photon defects (CD) due to focal parenchymal lesions or scars after a loss of function and the last groups of the single and multiple CD for a suggestion of the clinical usefulness. Regarding to measurement of normal renal size, the longest size of the kidneys were evaluated with 5 cm of a lead scale on the posterior renal image, and those were decided to the limits beteen 104.1 and 119.4 mm as comparison with the renal size of intravenous pyelogram (IVP) in 59 cases who were underwent $^{99m}Tc-DMSA$ and IVP concommitantly. Among 85 cases of PD in $^{99m}Tc-DMSA$ renal scan, the 61 (71.8%) were cases of a dilated pelvocalyceal system related with obstructive uropathy, meanwhile the 28 (27.0%) of 162 cases with CD were cases of obstructive and infectious uropathy. The probability of a presence of some uropathy in cases of CD were 99.3%, meanwhile that of the presence of CD in cases of some uropathy were 37.9%. Besides, there were some specific anatomical findings such as polycystic kidneys with symmetric enlarged kidneys with multiple CD and the kidneys of chronic renal failure and/or hypertension with symmetric small size in $^{99m}Tc-DMSA$ renal stan.